1. Field of the Invention
The present invention generally relates to clamp holders, and more particularly, to a magnetic clamp holder used for a mechanical arm.
2. Discussion of the Related Art
A mechanical arm generally includes a clamp holder for holding a clamping device that is mounted with one or more workpieces. The structure of the clamp holder will directly affect a positioning precision of the mechanical arm. Referring to FIG. 6, a clamp holder 10 used for a mechanical arm is shown. The clamp holder 10 includes two rotatable cylinders 11, a supporting element 13, two guiding elements 15, a plurality of ball bearings (not shown), and two positioning elements 17. The rotatable cylinders 11 are disposed at opposite ends of one side of the supporting element 13. The guiding elements 15 are disposed on the side opposite to the rotatable cylinders 11 and are positioned at opposite ends of the side, similar to the rotatable cylinders. The positioning elements 17 are assembled corresponding to the guiding elements 15. Each of the guiding elements 15 and each of the positioning elements 17 cooperatively define a clamp hole 19. The ball bearings are disposed between the guiding elements 15 and the positioning elements 17, and the ball bearings evenly surround each of the clamp holes 19.
In use, when a workpiece (not shown) is to be moved, the workpiece is fixed to a clamping device (not shown). The clamp holder 10 is placed above the clamping device. The rotatable cylinders 11 of the clamp holder 10 are rotated so that the clamp holes 19 positioning aim at positioning poles of the clamping device. Then, the clamp holder 10 is moved down to the clamping device, and the clamp holes 19 of the clamp holder 10 engage with the positioning poles of the clamping device. The ball bearings are driven to clamp the positioning poles of the clamping device by gas injected from the rotatable cylinders 11. The workpiece with the clamping device can be moved to a determined position (for example, a platform of a machine) with a help of the clamp holder 10. When the ball bearings are applied to stop clamping the positioning poles of the clamping device, the workpiece with the clamping device can be detached from the clamp holder 10 and disposed at the determined position.
However, an positioning precision of the clamp holder 10 is in the range of ±0.1 mm. Therefore, the positioning precision of the clamp holder 10 is relatively low and can not be used for a higher precision manufacturing. In addition, the ball bearings, the guiding elements 15, and the positioning elements 17 are easily abraded in the process of clamping the positioning poles of the clamping device, thus the positioning precision will be decreased easily.
Therefore, a new clamp holder is desired in order to overcome the above-described shortcomings.